1. Field of the Invention
This invention relates generally to turbomachines, and more particularly to an interstage seal assembly for a turbine or a compressor.
2. Description of the Prior Art
Turbomachines having bladed diaphragms with inner shroud segments supporting seal assemblies between stages of the rotor are well known in the prior art. Generally such sealing structure accommodates large transient thermal growths inherent in the machine, by being mounted to the shroud segments in a manner that constrains the seal to remain concentric with the rotor (i.e., prevents the sealing assembly from floating) yet permits concentric expansion and contraction. This is readily accomplished by having the seal holding structure define a plurality of cooperating radially extending guide slots angularly separated so that the seal holders having keys matingly received within the slots are prevented from floating movement. In practice it is preferred to have at least three such angularly disposed slots for receiving three mating keys in each separate arcuate segment of the seal holders.
Since the mating guide slots and keys engage only when they are properly concentric, they are, of necessity, assembled by placing them in such concentric orientation and then moving them towards each other axially to assume their engaged position. The seal holder in turn defines structure cooperating with a seal ring so that the seal ring can be slid circumferentially to its proper position and locked there as by a set screw or indexing pin.
As each half of the shroud is assembled in this manner, a complete circular seal holder and seal ring is provided when the two halves are secured together.
Seal holding assemblies typical of the above are shown in U.S. Pat. Nos. 3,529,904 and 3,829,233 having a common assignee as the present application. However, in each of the structures shown by these patents it is seen that the axial retention of the key or pin, associated with the seal holder so that it remains within the radial slot of the flange to prevent unrestrained circumferential movement of the seal holder and radial displacement to a position permitting non-concentricity with the rotor, requires separate structure specifically and solely for this purpose, i.e., pin 51 in U.S. Pat. No. 3,529,904 patent, which results in a multiplicity of parts and complexity of assembly eliminated by the present invention.